The present invention relates to a method of producing filter-tipped cigarettes.
Filter-tipped cigarettes are normally produced from double cigarettes, each formed by rolling a gummed strip of paper material about a group consisting of two cigarette portions separated axially by a filter twice as long as that of a finished filter-tipped cigarette.
The strips are normally rolled about said groups by means of a rolling device to which the groups are normally fed by an input roller with a number of peripheral seats. Each seat receives and retains by suction both a respective group, and a respective gummed strip with one end connected to the group, along a generating line of the group opposite the seat, and projecting rearwards from the group in relation to the rotation direction of the input roller.
U.S. Pat. No. 4,848,371 relates to a so-called "multiple-channel" rolling method.
Here and hereinafter, the term "multiple-channel rolling" is intended to mean a rolling method whereby each group is fed to a respective transfer conveyor by which it is fed along a respective rolling channel in turn traveling along a given path.
More specifically, as described in U.S. Pat. No. 4,848,371, the input roller transfers the groups successively to a central rolling device or drum substantially tangent to the input roller at a transfer station, and rotating, at a first given speed equal, at the transfer station, to that of the input roller, about an axis parallel to the rotation axis of the input roller. The central drum comprises a ring of peripheral transfer rollers, each mounted on the drum so as to rotate, in relation to the drum, about a respective axis parallel to the rotation axis of the drum, and so as to define, with a peripheral portion of the drum, a respective rolling channel moving at said first speed along a circular path. Each transfer roller presents a respective peripheral seat, which, by virtue of the central drum and the respective transfer roller rotating about their respective axes, travels through the transfer station together with and at the same speed as a corresponding seat on the input roller, and is supplied by the input roller with a respective group and strip, which it feeds along said respective rolling channel. At the end of the rolling operation, said seat receives the newly formed double cigarette and, in the same way as for pickup but in reverse, transfers it to a seat on an output roller.
The advantages of multiple-channel as compared with standard single-channel rolling are considerable in that the multiple channels not only provide for rendering rolling speed substantially independent of the traveling speed of the cigarettes, thus enabling faster production speeds, but also prevent total stoppage of the machine in the event of a cigarette being damaged inside the rolling channel.
One drawback of multiple-channel rolling, however, poses problems in the case of applications involving production speeds over and above a given limit. In fact, as a consequence of the manner, described above, in which each group and respective strip on the input roller are presented at the transfer station, the group is transferred to the seat on the respective transfer roller with the strip facing the latter seat and extending rearwards in relation to the traveling direction of the central drum.
Since the strip faces rearwards, winding of the strip about the respective group--which is performed by expelling the group from the seat on the transfer roller and rolling it on the surface of the transfer roller and on the respective strip along the respective rolling channel--can only be performed by rolling the group backwards in relation to the respective transfer roller, which in turn can only be achieved by rotating the transfer rollers in the same direction as the central drum, with the result that, at the transfer station, the speed of the central drum is added to that of the seat on each transfer roller, and the pitch of the seats on the input roller is much greater than the already relatively wide pitch of the axes of the transfer rollers about the periphery of the central drum.
The relatively wide pitch of the seats on the input roller, and consequently also on the output roller, poses serious drawbacks in that, on the one hand, at high production speeds, the traveling speeds of the cigarettes up- and downstream from the rolling drum are practically unsustainable, and, on the other, a relatively drastic and hence relatively complex pitch reduction is required along the filter assembly machine, prior to feeding the cigarettes to the input conveyor of the packing machine.